diff --git a/orsopy/fileio/base.py b/orsopy/fileio/base.py
index edfc28c6..e6d02371 100644
--- a/orsopy/fileio/base.py
+++ b/orsopy/fileio/base.py
@@ -244,7 +244,14 @@ def _resolve_type(hint: type, item: Any) -> Any:
                 else:
                     return hbase([Header._resolve_type(t0, item)])
             elif hbase is dict:
-                value_type = get_args(hint)[1]
+                try:
+                    value_type = get_args(hint)[1]
+                except IndexError:
+                    warnings.warn(
+                        "The evaluation of type hints requires key/value definition for Dict, "
+                        "if you want to use unspecified dictionaries use dict instead of Dict."
+                    )
+                    raise
                 try:
                     for key, value in item.items():
                         # resolve the type of any value in the dictionary
diff --git a/orsopy/fileio/data_source.py b/orsopy/fileio/data_source.py
index 1ed63642..7575edc2 100644
--- a/orsopy/fileio/data_source.py
+++ b/orsopy/fileio/data_source.py
@@ -8,7 +8,7 @@
 
 import yaml
 
-from .base import File, Header, Person, Value, ValueRange, ValueVector, orsodataclass
+from .base import ComplexValue, File, Header, Person, Value, ValueRange, ValueVector, orsodataclass
 
 # typing stuff introduced in python 3.8
 try:
@@ -66,7 +66,7 @@ class Sample(Header):
     composition: Optional[str] = None
     description: Optional[str] = None
     environment: Optional[List[str]] = None
-    sample_parameters: Optional[Dict] = field(
+    sample_parameters: Optional[Dict[str, Union[Value, ValueRange, ValueVector, ComplexValue]]] = field(
         default=None, metadata={"description": "Using keys for parameters and Value* objects for values."}
     )
 
diff --git a/orsopy/fileio/schema/refl_header.schema.json b/orsopy/fileio/schema/refl_header.schema.json
index baf2b2d5..b1115a67 100644
--- a/orsopy/fileio/schema/refl_header.schema.json
+++ b/orsopy/fileio/schema/refl_header.schema.json
@@ -168,47 +168,54 @@
         "probe"
       ]
     },
-    "Sample": {
-      "title": "Sample",
+    "Value": {
+      "title": "Value",
       "type": "object",
       "properties": {
-        "name": {
+        "magnitude": {
           "type": [
-            "string",
+            "number",
             "null"
           ]
         },
-        "category": {
+        "unit": {
+          "description": "SI unit string",
           "type": [
             "string",
             "null"
           ]
         },
-        "composition": {
+        "comment": {
           "type": [
             "string",
             "null"
           ]
-        },
-        "description": {
+        }
+      },
+      "required": [
+        "magnitude"
+      ]
+    },
+    "ValueRange": {
+      "title": "ValueRange",
+      "type": "object",
+      "properties": {
+        "min": {
           "type": [
-            "string",
+            "number",
             "null"
           ]
         },
-        "environment": {
-          "items": {
-            "type": "string"
-          },
+        "max": {
           "type": [
-            "array",
+            "number",
             "null"
           ]
         },
-        "sample_parameters": {
-          "description": "Using keys for parameters and Value* objects for values.",
+        "unit": {
+          "description": "SI unit string",
           "type": [
-            "object",
+            "string",
             "null"
           ]
         },
@@ -220,14 +227,27 @@
         }
       },
       "required": [
-        "name"
+        "min",
+        "max"
       ]
     },
-    "Value": {
-      "title": "Value",
+    "ValueVector": {
+      "title": "ValueVector",
       "type": "object",
       "properties": {
-        "magnitude": {
+        "x": {
+          "type": [
+            "number",
+            "null"
+          ]
+        },
+        "y": {
+          "type": [
+            "number",
+            "null"
+          ]
+        },
+        "z": {
           "type": [
             "number",
             "null"
@@ -248,23 +268,45 @@
         }
       },
       "required": [
-        "magnitude"
+        "x",
+        "y",
+        "z"
       ]
     },
-    "ValueRange": {
-      "title": "ValueRange",
+    "ComplexValue": {
+      "title": "ComplexValue",
       "type": "object",
       "properties": {
-        "min": {
-          "type": [
-            "number",
-            "null"
+        "real": {
+          "anyOf": [
+            {
+              "type": "number"
+            },
+            {
+              "type": "array",
+              "items": {
+                "type": "number"
+              }
+            },
+            {
+              "type": "null"
+            }
           ]
         },
-        "max": {
-          "type": [
-            "number",
-            "null"
+        "imag": {
+          "anyOf": [
+            {
+              "type": "number"
+            },
+            {
+              "type": "array",
+              "items": {
+                "type": "number"
+              }
+            },
+            {
+              "type": "null"
+            }
           ]
         },
         "unit": {
@@ -282,55 +324,69 @@
         }
       },
       "required": [
-        "min",
-        "max"
+        "real"
       ]
     },
-    "Polarization": {
-      "title": "Polarization",
-      "description": "The first symbol indicates the magnetisation direction of the incident\nbeam. An optional second symbol indicates the direction of the scattered\nbeam, if a spin analyser is present.",
-      "enum": [
-        "unpolarized",
-        "po",
-        "mo",
-        "op",
-        "om",
-        "mm",
-        "mp",
-        "pm",
-        "pp"
-      ],
-      "type": "string"
-    },
-    "ValueVector": {
-      "title": "ValueVector",
+    "Sample": {
+      "title": "Sample",
       "type": "object",
       "properties": {
-        "x": {
+        "name": {
           "type": [
-            "number",
+            "string",
             "null"
           ]
         },
-        "y": {
+        "category": {
           "type": [
-            "number",
+            "string",
             "null"
           ]
         },
-        "z": {
+        "composition": {
           "type": [
-            "number",
+            "string",
             "null"
           ]
         },
-        "unit": {
-          "description": "SI unit string",
+        "description": {
           "type": [
             "string",
             "null"
           ]
         },
+        "environment": {
+          "items": {
+            "type": "string"
+          },
+          "type": [
+            "array",
+            "null"
+          ]
+        },
+        "sample_parameters": {
+          "description": "Using keys for parameters and Value* objects for values.",
+          "additionalProperties": {
+            "anyOf": [
+              {
+                "$ref": "#/definitions/Value"
+              },
+              {
+                "$ref": "#/definitions/ValueRange"
+              },
+              {
+                "$ref": "#/definitions/ValueVector"
+              },
+              {
+                "$ref": "#/definitions/ComplexValue"
+              }
+            ]
+          },
+          "type": [
+            "object",
+            "null"
+          ]
+        },
         "comment": {
           "type": [
             "string",
@@ -339,11 +395,25 @@
         }
       },
       "required": [
-        "x",
-        "y",
-        "z"
+        "name"
       ]
     },
+    "Polarization": {
+      "title": "Polarization",
+      "description": "The first symbol indicates the magnetisation direction of the incident\nbeam. An optional second symbol indicates the direction of the scattered\nbeam, if a spin analyser is present.",
+      "enum": [
+        "unpolarized",
+        "po",
+        "mo",
+        "op",
+        "om",
+        "mm",
+        "mp",
+        "pm",
+        "pp"
+      ],
+      "type": "string"
+    },
     "InstrumentSettings": {
       "title": "InstrumentSettings",
       "type": "object",
@@ -760,6 +830,8 @@
           "enum": [
             "1/angstrom",
             "1/nm",
+            "1",
+            "1/s",
             null
           ]
         },
@@ -802,6 +874,8 @@
           "enum": [
             "1/angstrom",
             "1/nm",
+            "1",
+            "1/s",
             null
           ]
         },
diff --git a/orsopy/fileio/schema/refl_header.schema.yaml b/orsopy/fileio/schema/refl_header.schema.yaml
index d6682060..69959147 100644
--- a/orsopy/fileio/schema/refl_header.schema.yaml
+++ b/orsopy/fileio/schema/refl_header.schema.yaml
@@ -25,6 +25,35 @@ definitions:
     - name
     title: Column
     type: object
+  ComplexValue:
+    properties:
+      comment:
+        type:
+        - string
+        - 'null'
+      imag:
+        anyOf:
+        - type: number
+        - items:
+            type: number
+          type: array
+        - type: 'null'
+      real:
+        anyOf:
+        - type: number
+        - items:
+            type: number
+          type: array
+        - type: 'null'
+      unit:
+        description: SI unit string
+        type:
+        - string
+        - 'null'
+    required:
+    - real
+    title: ComplexValue
+    type: object
   DataSource:
     properties:
       comment:
@@ -289,6 +318,8 @@ definitions:
         enum:
         - 1/angstrom
         - 1/nm
+        - '1'
+        - 1/s
         - null
     required:
     - name
@@ -312,6 +343,8 @@ definitions:
         enum:
         - 1/angstrom
         - 1/nm
+        - '1'
+        - 1/s
         - null
     required:
     - name
@@ -394,6 +427,12 @@ definitions:
         - string
         - 'null'
       sample_parameters:
+        additionalProperties:
+          anyOf:
+          - $ref: '#/definitions/Value'
+          - $ref: '#/definitions/ValueRange'
+          - $ref: '#/definitions/ValueVector'
+          - $ref: '#/definitions/ComplexValue'
         description: Using keys for parameters and Value* objects for values.
         type:
         - object
diff --git a/tests/test_fileio/test_data_source.py b/tests/test_fileio/test_data_source.py
index 43fb6a93..1a956779 100644
--- a/tests/test_fileio/test_data_source.py
+++ b/tests/test_fileio/test_data_source.py
@@ -115,12 +115,14 @@ def test_creation_optionals(self):
             composition="Si | SiO2(20 A) | Fe(200 A) | air(beam side)",
             description="The sample is without flaws",
             environment=["Temperature cell"],
+            sample_parameters={},
         )
         assert value.name == "A Perfect Sample"
         assert value.category == "solid/gas"
         assert value.composition == "Si | SiO2(20 A) | " + "Fe(200 A) | air(beam side)"
         assert value.description == "The sample is without flaws"
         assert value.environment == ["Temperature cell"]
+        assert value.sample_parameters == {}
 
     def test_to_yaml_optionals(self):
         """
diff --git a/tools/header_schema.py b/tools/header_schema.py
index 683f5a81..7df7cc98 100644
--- a/tools/header_schema.py
+++ b/tools/header_schema.py
@@ -46,7 +46,7 @@ def schema_extra(schema: Dict[str, Any]) -> None:
     "type": "object",
     "properties": {
         "name": {"enum": ["<cname>"]},
-        "unit": {"enum": ["1/angstrom", "1/nm", None]},
+        "unit": {"enum": ["1/angstrom", "1/nm", "1", "1/s", None]},
         "dimension": {"dimension": "dimension of column", "anyOf": [{"type": "string"}, {"type": "null"}]},
         "comment": {"anyOf": [{"type": "string"}, {"type": "null"}]},
     },