Clean up dirty job from the DenKey

MatrixManager.cs

using System;
using System.Collections.Generic;
using System.Linq;

namespace ConsoleApplication2
{
    public class Program
    {
        static void Main(string[] args)
        {
            const int dimension = 10;
            var myMatrix = new MyMatrix(dimension);

            var max = myMatrix.MaxInDiagonal;
            var min = myMatrix.MinInDiagonal;


            Console.WriteLine($"\nMAX: [{max.Coordiante.Row}][{max.Coordiante.Column}] {max.Value}");
            Console.WriteLine($"MIN: [{min.Coordiante.Row}][{min.Coordiante.Column}] {min.Value}");
            Console.ReadKey();
        }
    }

    public class MyMatrix
    {
        private readonly int _matrixSize;
        private readonly Random _random = new Random();
        private readonly IList<MatrixLine> _matrix = new List<MatrixLine>();

        public MatrixLine MinInDiagonal => FindSecondMin();
        public MatrixLine MaxInDiagonal => FindMainMax();

        public MyMatrix(int matrixSise)
        {
            _matrixSize = matrixSise;
            FillMatrix();
            PrintMatrix();
        }

        private void FillMatrix()
        {
            for (var i = 0; i < _matrixSize; i++)
            {
                for (var j = 0; j < _matrixSize; j++)
                {
                    _matrix.Add(new MatrixLine
                    {
                        Value = _random.Next(10, 99),
                        Coordiante = new Coordinate
                        {
                            Row = i,
                            Column = j
                        }
                    });
                }
            }
        }

        private void PrintMatrix()
        {
            var temp = 0;
            foreach (var item in _matrix)
            {
                var output = $"[{item.Coordiante.Row}][{item.Coordiante.Column}]{item.Value} ";

                output = temp != item.Coordiante.Row ? $"\n{output}" : output;

                temp = item.Coordiante.Row;
                Console.Write(output);
            }
        }

        private MatrixLine FindSecondMin()
        {
            var diagonal = new List<MatrixLine>();
            for (var i = 0; i < _matrixSize; i++)
            {
                var value = _matrix.FirstOrDefault(q => q.Coordiante.Row == i && q.Coordiante.Column == (_matrixSize - 1) - i);
                if (value != null) diagonal.Add(value);
            }

            return diagonal.OrderByDescending(i => i.Value).Reverse().FirstOrDefault();
        }

        private MatrixLine FindMainMax()
        {
            var diagonal = new List<MatrixLine>();
            for (var i = 0; i < _matrixSize; i++)
            {
                var value = _matrix.FirstOrDefault(q => q.Coordiante.Row == i && q.Coordiante.Column == i);
                diagonal.Add(value);
            }

            return diagonal.OrderByDescending(i => i.Value).FirstOrDefault(); ;
        }
    }

    #region Types
    public class Coordinate
    {
        public int Column { get; set; }
        public int Row { get; set; }
    }

    public class MatrixLine
    {
        public int Value { get; set; }
        public Coordinate Coordiante { get; set; }
    }
    #endregion
}